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yamie_rider

Decomp. lever mishaps

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Has anyone wrecked there 250f of 426 by accidently pushing the decomp. lever . I have crashed on mine many times and the engine is still fine

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Try moving the decompression lever under the clutch perch. Kind of like the XR's position. This protects it if the bike tucks under on that side during a spill. It can't be good to hit the decompression lever while the engine is running (bent exhaust valve), and also having to buy the little lever/perch isn't good either. I did this change when I first got my WR and have never had a problem.

[ January 28, 2002: Message edited by: desertfoxx ]

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i know a lot of guys that ride with there decompression lever facing backwards.i guess if uncoordinated its hard enough to just stay in the upright position while riding and not crashing.last thing you need to worry about is which lever you need to pull.

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From my past research the WR/ YZ motoris not an interferance motor... so the valve(s) can be open and clear the piston. I still have not tried it.. but you should be able to hold the de-comp lever open without damaging any valves.

Also - flipping the lever over will help keep it out of harms way :)

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The whole idea of the de-compressor is to get the piston past TDC. If the valve doesn't hit the piston when starting, then it won't hit when running either. However, I am sure that it is not a good thing to do.

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Originally posted by Woodzi:

The whole idea of the de-compressor is to get the piston past TDC. If the valve doesn't hit the piston when starting, then it won't hit when running either. However, I am sure that it is not a good thing to do.

Makes sense to me, I always wondered if you timed it wrong, and lifted the valve just after ignition whether you'd damage the valve/seat area, thought it best not to find out!

:):D

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Lance Smails toasted his yz250f motor last year at washougal when he crashed on his decompression lever during a race.Don't know all the details but i have heard from yamaha guys it can be done.I yhink it would be a good idea to try and prevent it if at all possible. :):D:D:D

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the YZ guys seem to think that there is no danger in using the decomp lever during engine running. Some say they need to use it to bump start the engine when it stalls, and one guy said he uses his to kill the bike.

later,

Ronin

[ January 30, 2002: Message edited by: Ronin ]

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valves do hit pistons but its ususlly because weak springs and over reving.if your springs are really weak or way out of adjustment over reving motor will cause them to float[the vavle bucket actually looses contact with cam lobe as they pass top dead center]instead of stay tight against against cam as valve's momentum compresses spring farther than normal and that causes contact with piston.

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I was riding (and I shouldn't admit it) but at fairly low rpm I had a brain fart and pulled the release lever and felt a tapping on it. But I don't know if it was the valve train tapping on the valve or a piston tap. No apparent damage but it did make me wonder wassup.

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That tapping sensation was the exhaust cam lifting (or pushing, whatever) the right side exhaust valve away from the compression release rod and then letting it back up.

As the cam lobe comes off that valve bucket the spring pushes it back up against the compression release rod, which transmits that tapping sensation through the cable to the lever (and your finger).

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